The present invention relates to a bar code reader reading a bar code attached or printed on an article.
As shown in FIG. 9, a conventional bar code reader starts a reading operation when it detects, by the article detector 4 using a ray of light, that the tip of the article 2 conveyed by the belt conveyor 1 has come into the read area 3. Then, as shown in FIG. 10, it scans the bar code 6 on the article with the plurality of scanning lines 5 from the scanning means using a ray of light (not shown in the figure), reads information represented by the bar code 6 through receiving the reflected light of the scanning lines, and outputs the read result to an external device at the time when the article detector 7 using a ray of light has detected the end of the article 2.
One of the important parameters indicating the performance of a bar code reader is a number of readable bar codes per a unit time. This performance parameter indicates how many pieces of bar codes on articles can be read per a unit time, and the greater the number of readable bar codes, the greater the performance is.
Considering a reading operation of bar codes attached on articles conveyed one after another to the read area 3 by the belt conveyor 1. If the speed of the conveyor 1 is constant, the shorter the transport distance between articles is, the greater the number of articles that come into the read area 3. Therefore, the shorter the transport distance between articles is, the the greater number of bar codes that can be read, thus the performance of such a device is greater.
In a conventional bar code reader, however, when two or more articles come into the read area 3 the device can not decide which bar code on an article it should read, so that two or more articles can not be put in the read area 3 as shown in FIG. 11. Thus, the conventional bar code reader has a defect that the transport distance 8 can not be shorter than the length of the read area 3.